Climate and weather in France

Photo above : A perfect thunderstorm builds up over Paris on a hot summer's afternoon

   Bordered by four seas (the North Sea, the Channel, the Atlantic ocean and the Medi­terranean), by three mountain ranges (the Alps, the Jura and the Pyrenees), and the edge of the central European lowlands, France is a country with very diverse climatic conditions, resulting in very different weather patterns. When visiting France, it is often usful to consult the weather forecast! The variety of France's weather patterns is further complicated by ongoing climate change and global warming, which in recent years have lead to a surprising number of unexpected and extreme weather conditions.

Like many places on Earth, France has weather conditions that are strongly influenced by barometric pressure: low pressure tends to leave France open to the influence of the Atlantic airstream, bringing with it clouds and rain; but when a ridge of high pressure builds up over the heart of western Europe, a large part of France, sometimes even the whole country, can be protected from the prevailing westerlies under a vast covering of dry air, often accompanied by winds from the east.
In short, the weather in France is determined by the balance of power between oceanic weather systems from the west, and continental anticyclones from the east.
   It is the differing relative influence of these systems that determine the two main climate zones of France, and within these two zones the different sub-zones.
These zones can be seen in the map on the left. In the western and north-western half of France, stretching from the Belgian border to the Pyrenees, the climate is generally oceanic, In Atlantic and northern regions, the influence of Atlantic weather systems is predominant; but further south and east, the influence of Atlantic weather systems diminishes.  The zones on the map are not fixed: the map shows the dominant type of climate over the year,  but borders can move. For instance when strong weather systems move in from the Atlantic, virtually the whole of France enjoys (or otherwise, as the case may be) an oceanic climate.

In practical terms, this means that the western areas of France benefit from a mild climate, with moderate rainfall possible at all times of the year. The "oceanic" area, and notably Brittany, jutting out into the Atlantic, has a particularly mild climate, but can be quite rainy even in summer months - though this is not always the case by any means. The semi-oceanic area, also called the intermediate area, has less rainfall particularly in summer, as it is more often under the influence of continental high-pressure systems. This band includes the great cereal growing regions of France, Champagne, the Beauce (south of Paris) and the Midi Pyrenees region, round Toulouse.
The eastern side of France has a more continental climate, Apart from the mountain areas, it is generally drier than western France, with winters that are colder and summers that are hotter, for a given latitude, The south coast of France benefits from a continental climate moderated by the influence of the Mediteranean, generally drier than the rest of France, and without the cold winters of the rest of the continental climate zone.

The microclimate of the Riviera: the extreme southeast of France, the area around Cannes, Nice and Monaco, benefits from its own microclimate; protected from the Mistral by the mass of the Alps, the climate on this narrow coastal plain is pure Mediterranean, with mild winters and warm summers.

The mountain areas of France; like all mountain areas, France's mountain areas have a cooler climate than surrounding areas, with more precipitation. Since the wet winds in France are those that come from the west or to a lesser extent from the south, it is the southern and western sides of the mountain ranges that are wetter. This is particularly the case with the Massif Central, whose eastern half is drier. The Cevennes mountains, the south eastern part of the Massif Central, are generally quit dry, but can receive deluges of heavy rain if wet air moves up from the Mediterranean, which happens most often in the Spring or Autumn.
During summer, the upland areas of central southern France are generally warm and sunny, but dramatic skies can brew up on sultry summer afternoons, often developing into short but spectacular thunder storms.

In the Pyrenees, it is the French side of this range, i.e the north eastern side, that is wetter than the Spanish side. This is because moist oceanic air is pulled through southwest France from the Atlantic to the Mediterranean. In all the mountain areas of France, thunderstorms are a common feature in summer.

Moving Boundaries:

With the exception of the areas of mountain climate, which are determined largely by altitude and topography, the borderlines betwen the different climate zones of France are variable, and will move north and south, east and west, depending on the strength of conflicting weather systems. It is quite possible for the whole of France to come under the influence of the prevailing Atlantic westerlies, with their clouds and showers; conversely at other times the whole of France can be dominated by continental air masses, leaving hardly a cloud in the sky over the whole country.